Bio Bulletin 2

1) We know that in the tale of endosymbiosis, chloroplasts and mitochondria have prokaryotic origins and one of the main features is the presence of the double membrane. Hence does this make the nucleus a prokaryote in the distant past?


This question is unresolved at the moment. Reference:
http://www.sciam.com/article.cfm?articleID=000E9461-AB74-1C75-9B81809EC588EF21

(Extract)

The nucleus also has some superficial similarities to these organelles: a two-layered membrane surrounds them all; they each have their own genome; and they are capable of reproducing. "It's easy to get [these features] when you're essentially swallowing a symbiont," says Hyman Hartman, a research scientist at the Massachusetts Institute of Technology who studies the origin of life. "It doesn't take a rocket scientist to [suggest] the nucleus had an endosymbiotic origin."
Subsequent molecular data only fanned these speculative flames by revealing that the eukaryotic genome is a mixed breed. Genetic sequences indicate that eukaryotic genes for building and manipulating DNA, RNA and proteins seem to come from archaea, whereas genes for metabolism and other cellular functions likely hail from bacteria. "The heart of the problem is that the logic of the eukaryote is very different from the logic of the prokaryotic cell, yet there has been a huge input from the prokaryote to the eukaryote," Hartman says.
..............

Martin, however, points out a number of sticking points for any endosymbiotic model. First, although the membrane surrounding the nucleus appears similar to those of mitochondria and chloroplasts, all of which have two layers, the nuclear membrane is unique. It is a single layer folded on itself, its pores are much different from those in bacteria, and it disintegrates when the cell divides. Second, even though the enzymes that build DNA and RNA do their work in the nucleus, that doesn't mean their genes necessarily started out there. "The argument that the nucleus is an endosymbiont (given by a number of authors) is just not borne out by our knowledge of the structure and function of the nucleus," concludes Anthony Poole of Massey University in New Zealand.

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2. Meristem. Are they only found at the root tip?

Nope.

A meristem is a tissue in all plants consisting of undifferentiated cells (meristematic cells) and found in zones of the plant where growth can take place.

The following exist:
1 Shoot apical meristems
2 Root apical meristems
3 Stem apical meristem
4 Intercalary meristem
2.5 Floral meristem

Reference: http://en.wikipedia.org/wiki/Meristem

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Role of auxins + cytokinins. We know about how their relative ratio affect root and shoot growth. What about their individual self?

It is rather hard to classify because their effects are broad-based. You can see them as ligands but when they bind to receptors on different cells, diff responses will result because of...... (you should know)

But below may be the parts you are interested in:

"cytokinins are compounds that stimulate cell division or cytokinesis, although they may also do other things. Proper regulation of cell division also requires auxin, which is needed to cause DNA synthesis before a cell can divide."

Reference: http://www.bio.indiana.edu/~hangarterlab/courses/b373/lecturenotes/hormones/hormone1.html

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Branchpoint sequence (splicing)

To talk about this for splicing is really getting into the specifics which I do not expect students to know at this level but since this was mentioned, here is a good reference: www.devbio.com/ article.php?ch=5&id=50



To cut a long story short, there is a consensus sequence UAUAAC (branchpt) found within the intron that will cause the formation of a lariat (phosphodiester bond) as an intermediate and this subsequently still lead to the joining of the exons. This is a model proposed.

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Attenuation

This contributes to the termination of transcription in Prokaryotes.
Attenuation is means of controlling transcription of a particular mRNA through the formation of translation-dependent alternative RNA structures (-ve feedback)

Below shows attenuation in trp operon. In a nutshell, the mRNA can form various loops and when trp is high, a different RNA loop structure is formed to prevent complete transcription of all the genes in the operon.




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And yes. TATA box like the pribnow box are found on the non-template strand but such detail is not critical. Most of the references just req you to state that TATA box is found in promoter and promoter is upstream of the initation site. Do you know the significance of TATA box besides as a recognition site by RNA polymerase? Check your prelims answer.

so what about for the rest of control elements? It is less clear. It seemed to be possible to exist on either strands. then again the same advice apply. Doesn't matter.